Intercommunication system



y 24, 195] F. PEDATELLA INTERCOMMUNICATION SYSTEM Filed May 26, 1950INVENTOR. Frank Pedcliel [0 ATTORNL f5,

Patented July 24, 1951 UNITED STATES PATENT OFFICE I 2,561,946INTEROOMMUNICATION SYSTEM Frank Pedatella, New Kensington, Pa.

Application May 26, 1950, Serial No. 164,336

Claims.

This invention relates generally to communication systems, and moreparticularly to su h systems embodying a plurality of transducerstations which may be selectively connected together.

This invention, while primarily adapted for, and illustrated inconnection with, a direct wire type of intercommunication system,.embodies certain fundamental aspects which are useable in other types ofcircuits. However, it will be appr'eciated that in the illustratedsystem,-repre senting a preferred embodiment of the invention, a degreeof simplicity is achieved which is not to be found in more conventionalapparatus for the intended purpose.

' In the usual intercommunication system each master station is providedwith equipment including an amplifien'a transducer, usually in the formof a permanent magnet speaker, or, alternatively, a separate speaker andmicrophone, together with a push button station',-the push buttonstation being operated selectively to connect the corresponding masterstation with other master or staiT stations forming a, part of thesystem. Suitable relay switching means under the control of therespective master station push buttons establish the desired circuitconnections. W Each master station with its amplifying and switchingunits represents a complicated and expensive piece of equipment. As aconsequence, in installations embodying such equipment, the masterstation installations are limited to those points from which control anddirection of operation is to reside, while the remaining stations,usually referred to as stafi stations, are equipped only with atransducer unit completely under the control of the master stations.

In numerous instances, situations arise at the various stafi' stationswhich require contact with personnel at one or more master stations,.butwith such a system the staff personnel has no means through theintercommunication system for contacting the desired master stationpersonnel. This, of course, is a, limitaton which re stricts theeffectiveness of the system.

Accordingly, one object of this invention is to ,provide anintercommunication system of sim:

plifled and economical structure, a, system which may be installedeasily and operated readilysystem which is positive in operation. 7

Another object of this invention is to provide an intercommunicationsystem in which a cen-.- tral amplification system is employed. It isalso an object of this inventionto provide a system of the characterreferred to, whose ment of, the invention.

While it will be appreciated that the intercom- .munication systemillustrated in the drawin may incorporate any number of stations, fourstations are illustrated in this case, since the structure of theinvention and its operation may be fully understood with such showing.The four stations are shown respectively designated SI S2, S3 and S4.Each includes a transducer element illustrated in block diagram andidentified by the reference characters Ti through T4, respectively. Eachtransducer embodies conventional equip- .ment. For example, thetransducer'may consist of a standard permanent magnet speaker which maybe utilized to convert electrical signals to sound, and, conversely, maybe utilized to conv-ert sound or speech to electrical signals. A1-ternatively, of course, a transducer in each case may include a separatespeaker and a separate microphone suitably connected into the system forthe intended purpose. Other arrangements may be incorporated foraccomplishing the intended purposes, by means of other forms ofconventional apparatus.

Each xstation also includes a plurality of switches, one switch for eachstation. In station SI these switches are designated SH through SM. Instation S2 the switches are designated SZI through S24. In station $3the switches are designated S3! through S34, and in station S4 theswitches are designated SM through S44.

Selective switching for interconnecting the desired transducer elementsis accomplish-ed by a pair of switch assemblies M and SS. Switchassembly MSS is a master station selector switch, and switch assemblySS'is an auxiliary selector switch which-Works in conjunction with themaster selector switch MSS to provide connections between the desiredtransducers. Both switch assemblies are motor operated, switch MSS beingdriven by a, motor IM and switch SS being driven by a motor 2M.

Referring particularly to the master switch arrangement, the masterswitch includes four separate switching units, one for each switchstation. These separate units are shown as interconnected mechanicallyoperated switch stacks, having an operating member which rides on thesurface of a cam ii). This cam is circular in configuration and has asingle projection H thereon, which during cam rotation successivelyengages the operating members of the separate switch stacks, and therebyoperates these separate stacks. The cam is shown to be mechanicallyconnected to the motor IM, and this connection is to be understood toinclude a reduction gear assembly, if required. Control of the motor IM,which operates the separate switch units, is obtained by suitableinterlocking of the motor, circuit with normally closed switches iMlthrough wi l which are disposed on the respective switch units. Theseseparate switch units have a common terminal connected to one terminalof the motor IM, the other terminal of the motor IM being connected tothe line 2 of the power supply lines I and 2. These supply alternatingcurrent (although the apparatus may be designed for direct current) foroperating the system. A normal 110 volt A. C. power supply will do.

Each of the switch units of the respective switch stations isillustrated as a three terminal switch. Refer, for example, to theswitch SH. This switch includes the terminals or contacts Ila, Nb and Howhich are straddled by a mov able contact member which is push-buttonoperated, and which in its closed position, under manually appliedpressure, engages all three of the named contacts. The middle contact,Nb, of switch SH is connected to the power supply conductor l, andsimilarly the middle contact of each of the remaining switches of all ofthe stations is also connected with the power supply conductor I. Thus,in efifect, there are provided with the three terminals, two switcheswhich are simultaneously closed at the time the push-button is operated.

Control of the motor lM is obtained from the respective stations Sl-S4,by connecting certain switch terminals thereof to correspondingterminals of the respective switches designated 1M! through lM4. Forexample, the terminals Ha, l2a, Ilia and lid of station Si are connectedin parallel by means of a common conductor to one of the two contacts ofthe switch lMl. The corresponding terminals of switches S2! through S24of the station S2 are connected in parallel to one contact of switch!M2; the corresponding terminals of the switches S3! through S34 ofstation S3 are connected in parallel to one contact of switch 1M3; andthe corresponding terminals of the switches SM through S44 of station S4are connected in parallel to one contact of switch IM4. Th remainingcontact of each of switches iMl to [M4 are connected in parallel to oneterminal of the motor lM, as shown.

Returning to the switch Sli of station Si, it will be appreciated thatby depressing the push button of this switch a circuit is completed fromthe conductor 4 through the contact i lb and contact Ha to one contactof the switch IMI. Assuming that the cam 59 is in a position differentfrom that illustrated. it will be understood that n th contact IM! willbe in circuit-closing position. Thus, both contacts of the switch I Mlwill be electrically united, whereby electric supply line I is connectedto one terminal of the motor WI. The other terminal of motor lM ispermanently connected to the electric supply line 2. Thus, theenergizing circuit for the motor is completed.

The motor IM rotates in one direction only, which in this case isclockwise as viewed in the drawing. It will be understood that th cam Itwill be rotated until the projection H thereof engages the operator ofthe switch stack including the contact arm of switch I MI. At this pointthe switch IMI is opened and the energizing circuit for the motor lM' isinterrupted and the motor stops. The operation involving the control ofthe motor IM for the remaining switches S12 through SM on station SI isthe same, since closure of any one of these switches establishes anenergizing circuit for the motor through the contacts of switch iMl.Thus, regardless of which of the motor operating contacts on station Siis manually operated, the motor will always stop with the cam in theposition illustrated in the drawings.

This same type of operation is effected from any of the remaining switchstations. For exams ple, referring-to station S 1, the closing of switchS4! completes an energizing circuit for the motor !M, the circuitrunning from the conductor I through the contact Mb to the contact Ma,and from the latter contact through the two contacts of the closedswitch !M4 to on terminal of the motor !M, the circuit being completedfrom the other terminal of the motor I M to the conductor 2. Assumingthat at the time this energizing circuit is; completed the cam Ill is inthe position illustrated, the motor 1M will rotate the cam clockwise,until projection ll thereof engages the operator of the switch stackincluding the switch IMA'. At this time the contact IMA is opened andthe energizingcircuit for the motor is brokern From the foregoing itwill be appreciated that operationof any one of the push buttonshereinabove considered in the respective stations S l-S4 will causeoperation of the motor IM to actuate the switch unit corresponding tothe stationon which the particular push button switch has been operated,thereby eiiecting selective'operation'of the switch units of the masterswitch 'MMS.

As earlier noted herein, the auxiliary selector switch SS is operated bya motor 2M. The motor 2M is controlled by a switch arrangementcorresponding to the switch arrangement IMI through 1M4 of the masterswitch. This switch arrangement, which is hereinafter referred to as anauxiliary control switch, is generally designated ACS, comprisesindividual switches 2M! through 2M4 which are operated by a circular cam20 having a single projection thereon. The contacts of switches 2Ml-2M4are normally closed except when operated by the cam 20, and theserespective switches correspond to the correspondingly numbered switchesof the respective stations Sl-S4 as identified by the last digit of therespective reference characters. Thus, for example, switches S13, S23,S43 and 2M3 are corresponding switches. Switch S33 is omitted since itis the master switch on station S3. Similarly, switches SI I, S22 and SMare the master switches of the corresponding switch stations Si, S2 andS4. These last named switches are each connected in series withauxiliary control switch 2MA. Switch ZMA, which also is normally closed,represents the position in which the selector switch SS is to be stoppedfor the purpose of connecting a given transducer with all of the othertransducers of the system. This will be more fully describedhereinafter.

As the various switches above considered are identified on therespective switch stations, the 'last'digit of the reference characterindicates the particular station with which that particular switch isrelated. For instance, referring to the switch SI I, the last digit 1indicates that such "switch'is in station I, and by further examination,with regard to the switch Sl3, the last digit '3 indicates that bydepressing this switch the *transducer Tl may be connected with thetrans- "ducer T3.

In the system herein illustrated the switch which is numbered inaccordance with the number of the switch station in which it is located"is utilized to connect the transducer of that sta- -tion with all ofthe other transducers, by the 'control afforded through the contact ZMAof the auxiliary control switch ACS, thereby controlling the motor 2M insuch a, way as to position the selector switch SS to establishconnection of the remaining transducers. For example, by closing switchSH transducers T2 through T4 will be connected with the transducer Tl.In a similar manner on station S2 the push button switch S22 isconnected with the contacts 2MA to effect connection of the transducerT2 with all other transducers Ti, T3 and T4, while either the switchesS33, and S44 of the stations S3 and S4,

respectively, function in a similar capacity to connect thecorresponding transducers with all the other transducers of the system.

In accomplishing this function the contacts H0, 220, 33c, and 440,respectively, of the switches SI I, S22, S33and S44 are connected to onecon- .tact" of the switch 2MA, the other contact of which switch 2MA isconnected in common with all of the corresponding contacts of theswitches 2M! through 2M4 withone terminal of the motor 2M. The otherterminal of motor 2M is connected to the conductor 2. As in the case ofthe set of switches which control motor IM, each of the switches Sll-SMnow being considered in the respective stations S|-S4 is supplied withpower from the conductor I through each of centrally located contactsthereof (such as the contact l Ib'of switch SH of station SI). Theremaining switches of each of the stations Sl--S4 are utilized asearlier mentioned, to connect the transducer of that particular stationwith a correspondingly numbered transducer. This is accomplished byconnecting these respective switches in series with the correspondingone of theswitches 2M| through 2M4.

-For example, 'the'contact I20 of the switch Sl2 isconnected in parallelwith the contacts 320 and 420 of the switches S32 and S42, respectively,all of these contacts being connected to the remaining contact of theswitch 2M2 of the auxiliary control switch. Hence, for example, upon theoperation of puush button Sl2, a circuit is completed from conductor lto the power supply contact l2b, to the contact [20 of the switch Sl2,

to the contacts 2M2. From the common terminal of-these contacts, thecircuit continues through "the motor 2M to the conductor 2 whichcompletes the energizing circuit for the motor. Operation of the motorcontinues the rotation of the cam 20, until the cam projection opens thecontacts 2M2, at which time the motor circuit is broken and the motor 2Mis stopped.

*As illustrated, the motor 2M drives the selector switch SS as well asthe auxiliary control .switch ACS. The selector switch SS is comprisedof two separate switch sections, one of which'includes the separatecontacts SSI through SS4, and the other of which includes an incomplateannular or arcuate contacti25, havinga projection 26 thereonforengagi-ng a stationary contact designated SSA. This stationarycontact is electrically connectedto the movable switch element 21, bothelements being supplied with power through a circuit includingconductor; 21A, which willbe describedhereinafter; By means of parallelcontacts which engage the 'arcuate contact 25, each of the contacts SSIthrough SS4 is connected therewith'fiuThe movable switch opening 25a inarcuate contact. 25 straddles the stationary contact associatedtherewith corresponding to contact SS3. Thus this contact is effectivelydisconnected from the 'arcuate contact 25. Similarly, when the cam 20occupies any of the three remaining positions in which contacts SSI,SS2, andSS4 are engaged, opening 25a straddles the corresponding contactassociated therewith and" therefore the arcuate contact is effectivelydisconnected from the circuitin each of the four single.stationnpositions of the cam 20. In the all station position of cam 20switch'ZMA is opened on switch ACS; Movable contact' 2'lnow lies betweencontactsSSl and SS4'and projection 26 engages contact SSA connecting thearcuate contact to circuitQTA.

In this intermediate angular position of cam 20 the angular position ofthe arcuate contactis suchthat all four stationarycontacts associatedtherewith are engaged thereby to thus conn'ectall of thecontacts SSIthrough SS4 to conductor The various contacts SSlthrough SS4 of theselector switch SS are severally connected with certain correspondingcontacts of switches Cl through C4 of the master switch u'nit MSS: The

contacts of each master switch unit (II- 04mmprise a'transfer contactassembly having a normally closed back contact and a normally open frontcontact. For example, the contact SSI is connected with one of the twoback-contacts of the switch CI. The contact SS2=is "connected with oneof the two backcontacts of 'the switch C2. The contact SS3'is connectedwith one of the two back contacts of the switch C3, and

the contact SS4 is connected with one of the two back contacts of theswitch 04. The other back contact of each switch CIC4 is connected tothe corresponding' front' contact, and these commonly connected contactsare respectively connected to thecorresponding transducers Tl-T l. Forexample, transducer TI is connected' with the commonIront-back contactsof the contact assembly Cl, and the transducer'T2 is connected withthe'common front-back contacts of switch G2, etc.

It will be understood that each switch C1-C4 includes a pair of frontcontactsand a pair of back contactsand that'one front 'contact'and oneback contact of each of said'switc hes are connected together, and as'thus electrically paired are connected to the transducers TI to T4,respectively. As already noted, the back contacts of the switches C|-C4which are not connected in common to the respective transducers TI-T4are connected severally to the contacts SSI-SSQ, respectively, of theselector switch SS. The front contacts of the switches CIC4 which arenot connected in common to the respective transducers T|-T4 areconnected in common to the conductor CA leading to a reversing switch ofthe double-pole, double-throw type actuated by a relay R.

The circuit designated 21A, which energizes the movable element 21 andthe stationary contact SSA of the selector switch SS, is also connectedto the double-pole, double-throw reversing switch, and the circuits CAand 21A are connected together through an amplifier generally designatedA, having the input and-output circuits designated I and 0,respectively, which are also connected to the reversing switch.

The reversing switch is shown in its normal or deenergized position.This switch includes two contact arms RI and R2, each arranged with twosets of transfer contacts. The back contacts of each set of transfercontacts are normally closed as shown, and, upon energization of thecoil of the relay R, these contacts are opened and the front contactsthereof are closed. In the illustrated position of the reversing switch,the conductor CA is connected through the back contacts of the transfercontact assembly R2 to the output circuit of the amplifier, and theconductor 21A is connected through the back contacts to the transfercontact assembly RI to the input circuit I of the amplifier. Theseconnections as will be hereinafter described connect the transducer atthe station initiating a call with the output 0 of the amplifier andconnect the called station or stations to the input of the amplifier.Thus to transmit a message from the calling to the called station therelay R must be operated from the calling station. Suitable switchingmeans yet to be described is provided for this purpose at each station.While this mode of operation may be preferred for one application,-inother applications the reverse may prove more convenient in which casethe conductor CA will normally be connected to the input of theamplifier A and the conductor 21A connected to the output. This willconnect the calling station to the input I and the called station to theoutput 0. This; in practice, is ac- N complished by simply reversing thecircuits I and 0 from that indicated. Switching means at the respectivestations will again be provided to control relay R.

Assuming now that it is desired to connect the transducer 'II with thetransducers T3, the push button switch assembly SI3 of station SI isdepressed, connecting the contacts ISA and I30 with the energizingcontact l3b. A circuit is therefore completed for energizing the motorIM which is traceable from the supply conductor I to contact I3b, tocontact I3a, to the motor control contacts of switch IMI. Assuming forthe moment that the contacts of switch IMI are closed, themotor-energizing circuit is completed through these contacts and themotor IM to the conductor 2. The motor is therefore operated until theprojection II on cam I0 opens the switch IMI, at which time the motorcircuit is interrupted and the motor stops. If the cam should bepositioned as illustrated in the drawing at the time switch SI3 isclosed, the motor IM is not energized, nor need it be.

A circuit for operating the motor 2M is also established through switchSI3 from supply conductor i to energizing contact lab, to conthe motor2M to the supply conductor 2, thereby energizing such motor, androtating the cam 20 until the contacts of switch 2M3 were opened and themotor ale-energized. In view of the proper indexing and the commonrotation of the movable switch element 21 with respect to the cam 25,such switch element engages the contact SS3 of the selector switch SSwhen the motor 2M stops, and thereby completesa-circuit connecting thetransducer Ti with the transducer T3. This circuit extends fromthetransducer TI through the conductor TIA to the commonly connected frontand back contacts of the transfer switch Ci. The closing the pushiuttonswitch Sis having moved the cam I0 into the position shown in thedrawing, the front contacts of the transfer contact assembly CI areclosed and a circuit is established through these front contacts to theconductor CA connected thereto. From the conductor CA the circuit isconnected to the output circuit 0 of the amplifier A through the hackcontacts of the transswitch or contact assembly RE. From the outputcircuit 1 of the amplifier the circuit continues through the closed backcontacts of the transferswitch or contact assembly RI to the conductor213A, which is engaged by rotary arm r 27 to the contactSSE of theselector switch SS.

contact SS3 the circuit extends through the closed back contacts of thetransfer contact assembly or switch C3 of master switch MSS, thecommonly connected front and back contacts of which are connected to thetransducer Thus, by the provision of the individual master and auxiliaryselector switch assemblies MSS and ACS, the manipulation of the contactS13 automatically and quickly. interconnects the selected transducers Tiand T3. In this circuit connection, the transducer Tl is connected tothe output circuit of the amplifier A and the transducer T3 is connectedto the input circuit I of the amplifier. This circuit connectiontogether with a selective switching control. for the relay R, (at eachstation) provides means whereby the operator at station SI may convey amessage through the transducer TI to the transducer T3 without anynecessity of the party at the transducer T3 taking any action.

The selective switching control at station 'S is a push button operatedtalk-listen switch designated SiT, provided to control the energizationof the relay R. Depression of the push button sw' ch SiT energizes thecoil of the relay R in a circuit which is traceable from the supplyconductor I through the closed contactsof push button switch siT to theconductor TC, which is connected with the coil of relay R, and thecircuit is completed through the coil-of relay to the supply conductor2. This relay therefore picks up and closes the front contacts of therespective transfer contacts R! and R2, connecting the circuit CA withthe input circuit I and the circuit 27A with the output circuit 0, whichoperation, it will be appreciated, reverses the connection of thetransducers TI and T3 to the amplifier A, making it possible for theparty at station SI to converse with party at station S3.

All of the remaining switch stations are provided with correspondintalk-listen .push' but-v tons which are designated SZT, S3T.:and-S4T,respectively. Each of these are connected to the conductor TC and aretherefore in parallel with. one another and in series with the coiloftherelay Rf Hence, operation of anyone of these push buttons will energizethe relay, thus affording selective control of the reversing switchfromany one of the four stations illustrated.

.--Advantageously, I. provide means for visually indicating theestablishment of the circuits.be-'v tween any of the selectedtransducers vTl-T l upon'operation of any selected push button, and,also forindicating whether or not the system isbusy. Such indicatingmeans may be of any suitable form and in the illustrated embodiment;lightsare utilized to indicate these conditions.

-More particularly, each station. is provided with a busy light,respectively, designated .BLl, BL2, BL3 and BLA, and each station isprovided with. a pilot light which .indicatesthe establishmentofthedesired circuit. The pilot lights are..designated .PLl, vPLZZ, PL3.and PM, respec-,- tively. The control means for the busy light of eachtransducer is in the form of the-switch, which again may be a pushbutton switch, but preferably. a switch which when closed will re-, mainclosed. These switches. are respectively designated SIL, SZL, S3L andS4L. ,The busy lights BL! through .BL4 are, connected in parallel withthe conductors 2a and 2b, and any one of the switches SIL through S411;is adapted, whenclosed, to connect the conductor 2bto the supplyconductor 1, 5 Since the; conductor 2c, is connected to the .supplyconductor 2, it willbe appreciated that .the closin c,f,,,,any -0ne ofswitches SIL through S4L establishes an energizing circuit for-allofthebusy lights across the supply conductors I, and 2. Thus, the lightsbeing on atthe various stations indicate that the ,systemis presently inuse. The pilot lights PL! through PM are so connected into the systemthat they are illuminated only at the sta tion at which the operation isinitiated, inform: ing that part, when-the light is illuminated, thatthe desired circuit is completed. Hence-return ing to the. illustrationwherein. the push button sltjis operated, as above described, theoperator also closes the switch SlL,illuminating all of the bush lightsELI-BM, and at the same time establishin a partial connection forenergizing the pilot light PLI. j f L The pilot lights are controlledbytheswitches L| "through L4 of the master selector switch MSS. Thesepilot flight switches are v.:severally located on the individual contactstacks of the master selector switch, and are therefore selectivelyoperated with the respective switch stacks Qne contact of each switchLl--L4 is connected to the supply conductori, and the other contact iofeach of the light control switches. is connected in series withv thecorrespending pilot light (PLI PL4) and with the corresponding switch S1L-SJL) Thus. the pressing of the push button sis and .thefclosi'ng ofswitch 4 S IL- is effective through I the operation cream. [0 to' move.theISwitchQstackTIIMI, ol and LI' into the position shown; which, inaddition to interconnecting transducers TI and T3fas" already described;completes w en-elegai'rfg'circuit for the pilot light PLI of stationSl', said circuit extending from supply conductor 1 through switch SIL,through pilot light PL! and through the switch Lltosupply conductor-"2'.

Whileth'e light system is desirablefor= the 7 tratedI- At the same timea circuit for energizing' the motor 2M is completed from. supplyconductor 'l through the contacts Ilb, lie and conductor=C to theiunction point JA, and thence through the contacts'of switch ZMA 'of theauxiliary control switch ACS and through themotor' -2M to supplyconductor 2. Motor 2M therefore rotates cam 29 until the contacts ZMA:are opened and the operation of the mo-' ton interrupted. 5 B a -Withthecam 20 and switch elements thus positioned, the rotary switch arm 21 islocated between'the contacts SSl and SS4 of the selector switch!However, the projection 26 on the annular contact'25, which iselectrically united to all of the contacts SSI through SS4,

at this time engages the stationary contact SSA, wherefore all of theterminals SSI through SS4 are connected with the back contacts of thetransferswitches C2, C3 and C4 of the master selector switch MSS, whilethe switch CI stands removed from its backcontacts. The switches C2, C3and 04, as thus closed across their back contacts, complete the circuitsto the respective transducers T2, T3 and T4. While the back contactsofthe switch Cl stand'open, as shown, the frontcontacts of this switchare closed, thereby connecting transducer TI to transducers T2, T3andT4, the connection from the closed front contacts of switch CI oftransducer Tl extendingthrough line CA, switch R2, amplifier A,switch-Rl, line21A, contact SSA, engaged byprojection 26 onring 25, andthe conductors leading from said ring through the closed back contactsof switches C2, C3 and C4 to-thesaid transducers T2, T3 and T4. V

The ma'nipu1ation of the talk-listen switch SIT at station SI providesreversible communication between station SI and all of stations 82, S3and S4. As inthe case wherein transducer Tl was connected with thetransducer T3, the transducer TI is again connected to the outputcircuitof the amplifier A, while-the remaining transducersare-connected'to the input circuit thereofm' Although the amplifiercircuit will normally be reversed by operation of the switch'Sl T atstation SI, this circuit may also be reversed byoperation of any of theparallel connected switches S2T, S3T and S4T in the remaining switchstations- 5 -While the operation 0f the system'has been described'partby part with the development ofthe descriptionof the various components,a better understanding of the invention may be had from'a brief resumeof the operation of the system asa whole. For convenience in thisdescription, it will again beassumed that the transducer TFis-desired tobe connected with the transducer T3. 111' operating the-system theoperator at station 'Sl first depresses the light switch SIL toilluminate the busy lights: BLI through BL l. Thereafter the push buttonSI 3 is depressed and held down for an interval slightly longerthan-that required to illuminate the pilot light PLI. With thedepression of push. button SIS, the motor IM operates until the contactsIMI. of the master selector switch MSS are opened, which also opens theback contacts of the transfer switch Cl and closes the front contactsthereof, and at the same time closes the contacts Ll, which effects theillumination of the pilot light PLI. The clos ing of the switch Clconnects the transducer Tl through the then closed front contacts of thetransfer contact switch CI to the conductor CA which is connected to theoutput circuit of the amplifier A. The energizing circuit closed fromsupply line I through contacts I32) and I30 to the contacts 2M3 of theauxiliary control switch ACS energizes the motor 2M, which stops whenthe cam 20 opens the contacts 2M3. In this position of the cam therotary switch arm 21 engages contact SS3, and thereby completes anenergizing circuit leading from the input circuit I of the amplifier A,relay switch R1, line 21A andarm 21 to the closed back contacts of thetransfer, switch C3, and thence to the transducer T3, completing thedesired circuit between the two transducers TI and T3. I

From the foregoing it will be appreciated that any one of thetransducers TlT4 may be connected with any one of the remainingtransducers by simply manipulating a selected push button on thecorresponding station to effect the desired connection. Likewise any onetransducer may be connected to all of the remaining transducers byoperating the proper push button on that particular station.

It will be appreciated that the equipment at the respective stationsSl--S4 is both simple and inexpensive, including merely a transducerwhich may comprise a permanent magnet speaker commonly used for thispurpose, and a pushbutton assembly having a push-button for each stationof the system, together with a talk-listen push-button, and anindicating light switch, ifdesired. Elements such as these areinexpensive and are easily and conveniently arranged in an attractiveand compact unit.

The remaining components of the system: are also relatively simple andeasily manufactured. These components, for example the master switchMMS, the auxiliary selector switch SS, the auxiliary control switch ACS,and the electric motors IM and 2M therefor may be conveniently assembled.on a single base. The entire arrangement is small in dimension, whichmay, together with the single amplifier A be disposed at a convenientpoint in the system, where the various stations may be. easily wired andavailable for service.

With these few components it should be noted each station of the systemis a master station, where a person may converse at will with any one orwith all of the otherstations, without the need for personnel at any ofthe other stations to take part in the establishment of the circuits, orin the operation of the system for two-way communication. Thus, it willbe appreciated that in addition to the simplicity of the equipment, theequipment is highly flexible and at the-same time, very easily operated.

While cam-operated switches have been herein indicated for performingthe various switching functions, it will be appreciated by those skilledin the art that relay circuits may be readily substituted, therefor. Thepresent, arrangement in many instances will be preferred, since the costof equipment of the type herein 12 shown is a great deal less than thatof relay equipment. Furthermore, the unit assembly of the switches isrelatively compact.

The indicating light system may be elaborated, if desired, by connectingthe lights respectively in a circuit including in series therein, inaddition to the respective switches LI through L4, a corresponding setof switches on the auxiliary control switch ACS, each of which would beconnected in series with its corresponding switch Ll through L4, thecircuit being completed to the conductor 2 in exactly the same manner asthe present circuit for the switches LI and L4. With such an arrangementall of the series switches would of necessity be closed prior to thetime the pilot lights of the respective stations would be illuminated.

While a preferred embodiment of this invention has been illustrated anddescribed, it will be appreciated by those skilled in the art thatnumerous changes in the circuit and its components, and in thearrangement of these circuit components, may be made Without departingfrom the spirit of the invention defined in the appended claims.

I claim:

1. An interccmmunication system comprising a switching network forconnecting together a plurality of electrical transducers comprising incombination, a switch station for each transducer, each switch stationcompring a switch for each station; each switch having a first normallyopen contact and a second normally open contact, circuit meansconnecting said first contacts of each switch station in parallel,circuit means connecting the corresponding second contacts of theseparate switch stations in parallel, a master switch unit for eachstation; an auxiliary switch unit for each station; master switchcontrol circuit means connecting each master switch unit with theparalleled first contacts of the corresponding switch station, auxiliaryswitch control circuit means connecting each auxiliary switch unit withthe corresponding paralleled second contacts, circuit means connectingeach transducer with the corresponding master switch unit, and circuitmeans connecting the corresponding auxiliary switch units and masterswitch units.

An intercommunication system comprising a switching network forconnecting together a. plurality of electrical transducers comprising incombination a switch station for each transducer, each switch stationcomprising a switch for each station; each switch having a firstnormally open contact and a second normally open contact, each switchrepresenting at least one station other than the station at which hislocated, circuit means connecting said first contacts of each switchstation in parallel, circuit means connecting the corresponding secondcontacts of the several switch stations in parallel, and circuit meansresponsive to operation of any particular switch of a given station forconnecting the transducer of said given station to the transducer of thestation represented by said'particular switch. I

3. An intercommunication system comprising a plurality of transducers,a-master switch unit for'each transducer, an auxiliary switch unit foreach transducer, circuit means connecting each transducer to thecorresponding master -switch unit, circuit means connected in commonwith all the master switch units and all the auxiliary switch units,circuit means for individually connecting the master switch units to thecorresponding ,auxiliary switch units, and circuit cgsergeceir 13.means: for simultaneously actuating a selected master switch unit and aselected auxiliary switch unit.

4. Apparatus as said circuit means connected in common with all themaster and auxiliar switch units comprises an amplifier having aninputand an output circuit connected in series witheach of the master-switchunits and each of the auxiliary switch units.

' 5. Apparatus as set forth in claim Binwhich said :circuit meansconnected in common with.

all. .the master and auxiliary switch units comprises an amplifierhaving an input and an output circuit connected in series with each ofthe master switch units and each of the auxiliary switch units, areversing switch for reversing the connection of said input circuit andoutput circuit; and a separate switch for each transducer foractuating'said reversing switch. e .1

intercommunication system comprisin aplurality of transducers, a masterswitch unit for each transduceneach master switch unit having. a pair ofnormally open contacts and a pair or normally closed contacts, onenormally open contact'and'one normally closed. contact'of each ofsaid-pairs of contacts in each master switch unit having a commonterminal, circuit means connecting each transducer to saidcommonterminal of the. corresponding master switch unit,

an auxiliary switch having a pair of contacts, electrical conductormeans connecting all of the other normally open contacts of the severalmaster-switch units with one of said pair of contacts of-said auxiliaryswitch, circuit means connectingall of the other normallyclosed contactsof theiseveral master switch units withthe other of circuit, said inputcircuit being connected with all said other terminals of said normallyopen contacts and said output circuit being connected to said onecontact of said pair of contacts of said auxiliary switch, and areversing switch connected with said input circuit and said output 'circuit for reversing-the. connection of said 'inpu and output circuits. v

, 9,,A'I'i intercommunication system comprising a plurality'oftransducers, amaster switch unit foreach transducer, each master switchunitincluding a pair of normally open contacts and a pair of normallyclosed contacts, one normally open and one normally closed contact ofeach pair "of said contacts having a common terminal, an auxiliarycontrol switch assembly including an auxiliary switch for eachtransducer, each auxiliary switch having a pair of contacts for eachtransducer, each auxiliary switch having one contact of each pair ofcontacts connected in common, a selector switch connected to operate insynchronism with said auxiliary control switch assembly, circuit meansconnecting the transducers respectively to said common terminals of saidmaster switch units, control circuit means connecting each of the othercontacts of said auxiliary switches respectively to the other of saidnormally closed contacts of said master switch set forthin claim 3, inwhich 3, in which 14 IT unit's, 'circui't means connecting the othercontactof said selector switch with each of said othercontacts of saidauxiliary switches of the auxiliary control switch assembly, and circuitmeans for simultaneously operating a selectedmaster switch unit and anauxiliary switch of said auxiliary control switch assembly. I

10. Apparatus as set forth in claim 9, in which said control circuitmeans includes an amplifier. 11.- Apparatus as set forth in claim 9, inwhich said control means includes an amplifier having an "input circuitand an output circuit, and a reversing switch normally connecting saidinput circuit to the other contactsof said normally open contacts ofsaid master switch 'units', and means electrically connecting'saidoutput circuit to the-common-connected contacts of said auxiliaryswitches and to a contact of said selector switch. 1

-12.'Apparatus as set forth in claim 9, a cam foractuating the masterswitch units, a motor for driving said eam, switch means on each masterswitch unit for controlling said motor, and con trolcircuit meansselectively connecting each of said switch means and said motor inseries.

'13. A-pilot-light circuit for an intercommunication system comprisingthe combination of a plurality of transducers, a masterselector switchhavinga plurality of master switch units severally connected tosaidtransducers, anauxiliary control switch assembly having an auxiliaryswitch unit for each transducer connected with a corresponding masterswitch unit, a switch station for-each transducer including a switch foreachtransducer, all the switches of each switch station being connectedwith the corresponding master switch unit and the corresponding switchesof each .station being connected with the corresponding auxiliary switchunits, a pilot light for "bination of a plurality of transducers, amotor operated master switch unit for each transducer;

a motor operated auxiliary switch unit for each transducer, circuitmeansconnecting the corresponding. auxiliary switch and master switch units,circuit means connecting eachtransducer With the corresponding masterswitch unit, and switching means for each transducer for controlling themotor-operated master switch unit for controlling the motor operatedauxiliary switch unit.

16. In an intercommunication system, the combination. of aplurality ofspeaker-microphone stations each having individual switch unitscorresponding in number to the number of said stations, a master switchassembly comprising a plurality of master switch units corresponding innumber of the number of said stations, an auxiliary switch unitcomprising a plurality of auxiliary switch units corresponding in numberto the number of said stations, circuit means responsive to operation ofany one switch on one of said stations for operating the correspondingmaster switch unit, circuit means responsive to operation of any one ofthe corresponding switches on the different stations for operating thecorresponding auxiliary switch unit, circuit means connecting eachspeakermicrophone unit with the corresponding master switch unit, andcircuit means connecting each auxiliary switch unit with thecorresponding master switch unit.

1'7. In an intercommunication system for selectively connecting togethera plurality of electrical devices, the combination of a switch stationfor each device having individual switch units corresponding in numberto the number of devices, a master switch assembly having a plurality ofmaster switch units corresponding in number to the number of switchstations, an auxiliary switch assembly having a plurality of auxiliaryswitch units corresponding in number to the number of said switchstations, circuit means responsive to operation of any one switch of oneof said stations for operating the corresponding master switch unit,circuit means responsive to operation of any one of, the correspondingswitches of the different switch stations for operating thecorresponding auxiliary switch unit, circuit means connecting eachelectrical device with the corresponding master switch unit, and circuitmeans connecting each auxiliary switch unit with the correspondingmaster switch unit.

18. In an intercommunication system for selectively connecting togethera plurality of electrical transducers, the combination of a switchstation for each transducer having an individual switch unit for eachtransducer, a master switch assembly having a master switch for eachtransducer, each master switch unit having a normally open contact and anormally closed contact, an auxiliary switch assembly having anauxiliary switch unit for each transducer, a common circuit for eachnormally open contact of the jaster switch units, a common circuit forthe auxiliary switch units, circuit means connecting said commoncircuits together, circuit means connecting each transducer to thecorresponding normally open and normally closed contacts of the masterswitch units, circuit means connecting each auxiliary switch unit withthe corresponding normally closed contact of each master switch unit,circuit means connected With each switch station and responsive tooperation of any one switch of one of. said stations for operating thecorresponding master switch unit, and circuit means responsive tooperation of any one of the corresponding switches of the differ-- entswitch stations for operatin the correspond-- ing auxiliary switch unit.

19. In an intercommunication system for selectively connecting togethera plurality of electrical transducers, the combination of a switchstation for each transducer, each switch station comprisin one switchfor each station, each switch having; pair of normally open contacts, amaster switch unit for each switch station, an auxiliary switch unit foreach station, circuit means connecting the corresponding contacts on theseveral switch stations in parallel, circuit means connectin the.remaining. contact of each switch in parallel with correspondingremaining contacts of the switches on theother switch stations, controlcircuit means for each master switch unit connected with the paralleledcontacts of corresponding switch stations, control circuit means: foreach auxiliary switch unit connected with the corresponding paralleledremaining contacts of the separate-switch units, circuitmeans-connecting the corresponding master switch units and auxiliaryswitch units together, and circuit means connecting each transducer withthe corresponding master switch. unit.

20.v In an intercommunication system, the combination of a, plurality ofstations each including a speaker-microphone and. a push-button controlhaving push-buttons corresponding in. number to the number of stations,a pair of contacts for each push-button, a master selector switchincluding, a switch stack. for each station, each switch stack: having,a normally closed con tactv and a normally open contact, an auxiliaryselector. switch including a switchstackfor each. station, an amplifierhaving an. inputcircuitand.

an output circuit, means. connecting each speaker-microphone with thenormally open contact of the corresponding master switch stack, circuitmeans connecting each normally open contact of said master switch withoneof the circuits of said amplifier, circuit means connecting eachswitch stack of said auxiliary switch with the other circuit of saidamplifier, circuit means.

connecting each switch stack of said auxiliary switch in series with thecorresponding normallyclosed' contactv of said. master switch. and with.the correspondin speaker-microphone, actuate ing means for the masterswitch. for selectively actuating the switch assemblies of the masterswitch in response to operation of any one. push button on therespective: push-button controls. and second actuating means forselectively actuating any one switch stackof said. auxiliary switch inresponse to operation of. correspond-- ing push-buttons of. the"respective push-button controls.

FRANK PEDATELLA.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED- STATES. PATENTS Number Name Date 2,162,369 Campbell June 1.3',1939 2,162,370 Campbell June13, 1939'. 224:9,4-56 Campbell Apr. I8, 19412,269,144 Campbell Jan. 6; 1942 2,347,079 Campbell. Apr. 18;, 1944.2,496,159 'Hagens' Jan. 31, i950

